Some modifications of the stannous chloride reduction method for the estimation of inorganic phosphate reported by Berenblum-Chain are suggested. By this method, it is possible to measure 25 g l–1 of phosphorus /P/ as inorganic phosphate in the presence of macromolecules like deoxyribonucleic acid /100 g ml–1/, as compared to 200 g l–1 of P by the original method. If a larger sample volume /30 ml/ is used, even 5 g l–1 of P can be measured.